Voltage-controlled oscillators (VCOs) are used in phase-locked loops (PLLs) and like circuits to generate a clock signal. In order to achieve good rejection of supply noise, the VCOs are usually supply regulated. One technique for regulating the supply of a VCO is the use of a replica compensated linear regulator that provides both noise rejection and controls the frequency of oscillation.
One characteristic of a VCO is the gain (Kvco), which measures the sensitivity of the output frequency to input voltage, With newer fabrication technologies, the allowed supply voltage is decreasing while the VCO frequency requirement is increasing. This causes the gain of the VCO to increase with each new technology node. Higher VCO gain leads to higher deterministic jitter on the output of the application circuit, such as a PLL, due to noise on the VCO control voltage, Higher VCO gain also requires a larger filter capacitor in the loop filter depending on the PLL application, which requires more implementation area.